1. Field of the Invention
The present invention relates to an antiskid control device for vehicles, in which a skid of the wheel resulting from the locking of the wheel is prevented from occuring, the locking of the wheel taking place when a vehicle is braked upon running and the braking pressure exceeds the value matched with the coefficient of friction between the wheel and the road surface.
2. Description of the Prior Art
In the conventional antiskid control devices of this type, the vehicle body speed is detected and the wheel speed is maintained at, say, about 80 % of the vehicle body speed to attain an instantaneous control of the braking operation. One of these control devices detects the wheel speed and performs a speculative control of the braking operation for preventing the locking of wheel. That is, in order to avoid the locking of wheel, the wheel speed is momentarily memorized just before braking, there is obtained a reference speed for the imaginary vehicle body speed obtained by decreasing the memorized wheel speed according to a predetermined control pattern, and the actual wheel speed is compared with the reference speed. In addition, a certain number of different control patterns of the type described above are incorporated preliminarily in the control device, the road surface conditions are observed by a deceleration sensor (hereinaftr referred to as "G sensor"), and on the basis of the results of observation by the G sensor the braking operation is controlled speculatively at all times so that the braking pressure is increased and decreased in accordance with such factors as the changes of the coefficient of friction between the wheel and the road surface and the like. However, in the conventional control device having the above construction, although the time when the braking pressure applied to the wheel is released is adjusted in accordance with the changes in the road surface conditions, no consideration is given to the braking pressure increasing rate at the time of the reapplication of braking pressure to the wheel. Therefore, the braking pressure increasing rate is constant, with the result that the braking pressure often fluctuates within an unnecessarily wide range thereby increasing the braking distance. This constitutes a serious disadvantage.